Odd coincidence, this week I brought home several non fiction WWII books from the library including some submarine history. So when the recent discussions about how realistic the constant air attacks in the stock game were started, I just happened to have a couple of reference books on hand. I'm only up to 1943 in SILENT VICTORY, but there are several mentions of air attacks when cruising in the open ocean - all by "friendly" planes, mostly US Army Air Corps.
All enemy air attacks in the book were while in contact with enemy surface ships, which would make sense - air patrols over task forces and convoys would obviously take priority over patrolling the empty sea.
Some stats on the 52 US subs lost from another book, FINAL PATROL, which was published in 2006. After the war was over and historians could examine Japanese records the number of unknowns was reduced, and later discovery of some wrecks helped with the mystery of the deep minefields in Japanese home waters.
Losses by cause;
Friendly aircraft - 1
Friendly destroyer - 1
Ran aground - 4
Collision with friendly ship - 1
Own torpedo (circular run) - 2
Enemy mines - 6
Enemy sub - 1
Enemy aircraft - 5
Enemy surface ships - 16
Combined enemy aircraft and surface ships - 7
Unknown - 8